Obtaining tensile strength and fracture energy of brittle rocks using AUSBIT - Advanced universal snap-back indirect tensile test

Accurate determination of tensile strength and fracture energy in brittle rocks remains challenging because conventional indirect tensile tests cannot reliably capture post-peak behaviour or identify the onset and completion of fracture under unstable conditions. Under such uncontrolled failure, the obtained fracture energy is unreliable, particularly when the material exhibits class-II behaviour. This behaviour is characterised by a snap-back post-peak response, in which both load and vertical displacement reverse. Snap-back occurs when elastic energy stored in the specimen exceeds what the fracture process can consume. Therefore, stable cracking can be maintained only if this excess energy is removed. This study presents an experimental analysis framework for tracking fracture progression and completion within the Advanced Universal Snap-Back Indirect Tensile (AUSBIT) test. In AUSBIT, the specimen's lateral displacement is used as a control variable to adjust the vertical displacement so that a constant lateral displacement rate is maintained. This stabilises snap-back and allows crack propagation to be followed over extended timescales. Acoustic Emission (AE) monitoring detects abrupt changes in released energy associated with complete crack separation, while Digital Image Correlation (DIC) provides full-field strain evolution. Together, the two techniques enable consistent identification of key fracture stages. Tensile strength measured using AUSBIT is lower than that from traditional Brazilian tests, and closer to values expected from direct tensile testing. The fracture energy compares well with that from three-point bending tests under direct displacement control. The findings show that AUSBIT can determine both tensile strength and fracture energy of brittle materials from a single Brazilian disc specimen.